VALVE ACTUATING MECHANISM
A mechanism for actuating an engine poppet valve includes two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the stem of the valve, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. In the invention, an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, and a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem. The latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.
The invention relates to an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. Such valve actuating mechanisms are known per se and are described for example in U.S. Pat. No. 6,854,434, GB Pat. Appln. No. 0519876.7, and U.S. patent application Ser. No. 11/284,725.
BACKGROUND OF THE INVENTIONIn addition to controlling engine valves to vary such parameters as phase, valve lift and event duration, cylinder deactivation is becoming increasingly common on large displacement gasoline engines, where significant fuel economy improvements can result from running an eight cylinder engine on four cylinders during light load operation. Deactivating one of a pair of intake valves on a diesel engine in order to control in-cylinder swirl levels is also an interesting concept for future research.
OBJECT OF THE INVENTIONThe present invention therefore seeks to provide a system for controlling valve lift and duration which is additionally capable of deactivating one or more valves per cylinder.
SUMMARY OF THE INVENTIONIn accordance with the present invention, there is provided an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams, characterised in that an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.
In the invention, two cams are used to actuate one or more valves via a summation system, and the valve lift characteristic can be changed by phasing one of the cam lobes relative to the other. Such systems can be arranged such that valve lift will only occur when both cam lobes are on lift and the valve will be closed if either of the cam profiles is on its base circle radius. It follows that there will be some clearance in the system during some portion of the camshaft cycle when both cams are close to their base circle radii, and it is this clearance that provides the opportunity for a valve deactivation system to operate.
Many valve deactivation and cam switching devices are known from the prior art that are designed to operate when the valve is closed (e.g. U.S. Pat. No. 6,196,175 US 2002/0014217 U.S. Pat. No. 6,135,074) but in conventional systems where there is little or no clearance when the valves are closed the switching of the valve deactivation system has to be carefully controlled in order to prevent the switching process from taking place when the valve begins to lift. This would be likely to cause overloading of the locking components and damage to the system. In order to avoid this, the switching of the systems applied to each cylinder of the engine is often controlled independently to make sure each cylinder switches fully whilst the valve is closed.
Unlike conventional valve train systems, the summation rocker system design requires the rocker system to move whilst the valve is closed and the system is not heavily loaded. This allows a number of different implementations of the present invention, in which use is made of this additional rocker motion to effect the switching of the rocker system to a deactivated mode of operation. This allows the timing of the switch to be controlled such that it will always occur whilst the valve is closed and also offers the opportunity for the deactivation system to be integrated into the design of the rocker system rather than being a totally separate system.
The different embodiments of the invention, which will be described below, offer the following advantages as compared with prior art systems, namely:
-
- Additional valve train flexibility for advanced combustion strategies,
- Valve deactivation occurs only whilst the valve is closed,
- Valve deactivation and lift control systems can be integrated instead of being separate, and
- The invention can be implemented in different ways to suit a wide variety of engine architectures.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
The drawings in this specification are derived from complete technical engineering drawings which show different practical implementations of the invention in more detail than is necessary for an understanding of the invention. The function of many of the components will be self-evident to the person skilled in the art and the description of the drawings will therefore be confined mainly to an explanation of the way in which valve deactivation is achieved.
Two different types of summation valve train have been considered for the application of valve deactivation systems as shown in
In the valve train of
By varying the phase of the cams acting on the two rockers relative to one another, it is possible to vary the overlap period and hence the event duration. The phase of the valve event can be varied by altering the phase of both cams relative to the crankshaft.
The rocker system is not stationary during the clearance phase of the motion, but moves from its valve closing position back to its valve opening position. The proposed designs utilise the clearance in the system and the movement of the rocker system in the clearance phase to effect the valve deactivation.
A number of different locations can be selected for integrating a valve deactivation systems into the summation valve trains shown in
In the first embodiment of the invention, shown in
The rocker design shown in
The deactivation system is integrated into a clearance adjuster 50, which is mounted in the end of the rocker 12 and acts on the valve tip. The adjuster 50 comprises a hollow plunger 52 that can slide into the end of the rocker 12 and is biased into contact with the valve stem (not shown in
The valve is deactivated by applying oil pressure to a drilling in the rocker, which acts to force the central ball downwards against the action of the spring 54. The central ball 56 can only move when there is clearance between the rocker and the valve tip because it has to force the small balls away from the centre in order to pass through. The movement of the small balls pushes the plunger out of the rocker slightly due to the angle of the face on which they locate and this can only happen when the plunger is unloaded. The spring 54 also acts to move the plunger axially to a position where the small balls 58 can move freely.
When the rocker next contacts the valve, the plunger 52 will push the small balls inwards and retract freely into the rocker 12. If the oil pressure is removed, the large ball will move back against its stop under the action of the spring 54 the next time the system is in clearance. The contact of the small balls 58 on the larger ball 56 ensures that there are only two stable equilibrium positions, with the large ball being held against its upper stop, or against its retaining clip.
The latching system is an over-centre arrangement which cannot operate when the rocker is in contact with the valve tip, hence the switch between valve lifting and valve deactivation modes can only occur during the clearance part of the valve train cycle.
The system is also of a bi-stable design in that if the rocker is brought into contact with the valve whilst the system is in the process of switching, the contact forces the system into one or other of its stable positions. This avoids any extremely high forces being applied to the components of the latch.
This design can be applied to one or both valves of a pair, depending on whether single valve deactivation or cylinder deactivation are required. It would also be possible to switch a pair of valves independently if two separate switched oil feeds were provided—one for each rocker. Although it has been drawn for an OHC application, this design could be simply applied to a pushrod valve train system to achieve valve deactivation. In all cases a control spring is still required to maintain contact between both cam profiles and their respective followers.
An alternative design for the mechanism of
The embodiment of
A first method for achieving this objective is shown in
When the latching lever 72 is moved towards the valve, springs 80 between itself and the latching plate 82 become loaded, and the latching plate 82 will rotate on its pivot as soon as the system is in the clearance portion of the motion. As the system moves back towards the beginning of the valve lift, the lower section of the key 78 on the sliding cylinder 76 moves past the latching plate 82 and simply slides up into the rocker 12 rather than lifting the valve. A further spring 84 acts on the top of the sliding cylinder in order to maintain contact with the valve tip.
If the lever 72 is moved just as valve lift is about to commence, the latch plate 82 may not move quickly enough the avoid contact with the key on the sliding cylinder. In this case, the latch plate 82 will be forced back to its seated position in contact with the underside of the rocker body against the action of the two springs, and no damage to the moving parts will occur.
There will clearly be some movement of the latching lever 72 relative to the control shaft 70 during the operating cycle of the rocker, but this does not cause a problem as it is the position of the lever in the valve seated position that determines whether or not the valve will be deactivated.
An alternative mechanical valve deactivating system is shown in
Each rocker is fitted with a lever 96, the position of which determines whether the valve lift will be deactivated. Positioning of the lever 96 close to the pivot point of the rocker 12 minimises its movement relative to the static parts of the cylinder head and a number of fairly simple methods for moving the levers are feasible. One such method is shown in, and will be described below by reference to,
The different views in
An interlock system is provided to ensure that any change from valve activation to valve de-activation may only occur during the clearance phase of the rocker motion. This is achieved by a pin 104 that is fitted to the plunger 94 and passes through a slot 106 in the rocker body, into a profiled slot 108 in the sliding plate 98.
The plunger 94 is loaded by a spring 110, so that as clearance appears in the rocker system, the plunger will move out of its bore and the pin 104 will move to the bottom of the ‘V’ profile of the slot 108, rotating the plate to a ‘central’ position between the locked and unlocked positions. As the system approaches the point of valve lift, the clearance reduces and the pin travels up one or other side of the ‘V’, moving the plate into one of its extreme positions.
The movement of the plate 98 is determined by a torque spring 112 that acts on the pivot pin 92 of the plate 98 and reacts against the control lever 96. Moving the control lever therefore determines the direction in which the plate is preloaded by the torque spring 112, and this in turn determines whether the interlock pin 104 will move up the short or the long side of the ‘V’ slot.
A similar deactivation system can be applied to an engine using bridge pieces to transmit the lift of a single rocker to a pair of valves. The bridge piece design is particularly popular for engines using ‘twisted’ or ‘diamond pattern’ valve arrangements (as shown in
The design of the valve-lifting rocker may be described more easily with reference to the different views of
All the embodiments described above have operated on the principle of decoupling the valve actuating rocker from the valve stem, that it is say allowing the rocker to oscillate without transmitting its movement to the valve. There are however other ways of integrating a valve deactivation system into a summation valve train such as by decoupling the rockers from one another, decoupling the rockers from the cams or push rods or by forming one of the rocker of two parts that can be selectively locked to one another.
The embodiment of
The latching system 210 is designed to transmit rotation in only one direction. This is achieved by forming an end surface 214 of a latch pin 212 (see
Valve deactivation is achieved by holding the latch pin 212 in its disengaged position so that it is unable to re-engage under the action of the spring 216. Two different methods for doing this are illustrated in
A similar arrangement is possible for the OHC design where the supporting rocker 314 may be divided into a number of sections (314a, 314b and 314c) as shown in
A number of possibilities exist for locking the outer linkages such that they rotate with the centre section of the location rocker, including a latch pin design as described above. Alternatively a different connection system may be used as will be described below by reference to
As shown in the exploded view of
The locking arrangement can be seen more clearly in
The stepped locking pins 312 need to be retained in a suitable angular alignment in order to engage properly, so each is provided with a slot 320 into which is engaged a ball 322 to limit the angular rotation of the pin 312 (see
It can be seen from
The embodiment of
The operation of the valves is controlled by the rotation of the control shaft 452, but it is not necessary for all of the valves to be deactivated at the same time. By producing the control shaft 452, as shown in
The principle of integrating a control spring with the valve deactivation system can also be applied to an OHV system by integrating the control spring and the deactivation system into the cam follower assembly.
An alternative design for integrating a deactivation system into a cam follower is shown in
The internally splined component 612 has a helical groove 614 machined into its outer diameter, which is engaged by a ball 616 that is permanently fitted to the body of the cam follower. Oil can be supplied to the cavity below the internally splined component in order to move it to a higher position and this also causes it to rotate because of the helical groove 614. When the lower splined component 612 is held in this upper position, the upper spline can pass through it without making contact. When the lower splined component 612 is in its lower position, the two sets of splines are misaligned and so the upper spline cannot enter the lower spline.
The lower splined component 612 can only move to its upper position when the valve train is in the clearance portion of the cycle and the cam follower is fully extended. If it should be in the process of movement when it comes into contact with the upper spline, it will simply be forced back into its bore and take up the locked position.
A pair of slots in the bore of the follower locates the upper spline 610 and allows it a small range of angular travel. It is preloaded against one side of these slots by a torque spring 618 that is located beneath it in a housing 620, which also engages into the slots in the follower bore. This allows the upper splined component 610 to rotate with the lower spline when the pair are engaged and the lower spline is forced back into its bore under the action of the cam lift.
Claims
1. An internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including
- two rotatable cams,
- a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and
- a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams, wherein
- an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem,
- a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and
- the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.
2. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and both valves are adapted to be deactivated simultaneously.
3. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and only one valve of the pair is capable of being deactivated.
4. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and each valve of the pair may be selectively deactivated.
5. An internal combustion engine as claimed in claim 3, wherein the rocker system actuates a pair of valves, and deactivation one valve of the pair alters the lift characteristic of the second valve.
6. An internal combustion engine as claimed in claim 1, wherein a plunger is mounted in a rocker in such a manner as to permit the plunger to be retracted into the rocker in order to deactivate the associated valve and the latching mechanism serves to inhibit retraction of the lash adjuster so as to cause the valve to be actuated by movement of the rocker.
7. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is hydraulically operated.
8. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is mechanically operated.
9. An internal combustion engine as claimed in claim 6, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.
10. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.
11. An internal combustion engine as claimed in claim 1, wherein one of the rockers is formed of two sections that are pivotable relative to one another, one section being cam actuated and the other serving directly or indirectly to actuate a valve, pivoting of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve.
12. An internal combustion engine as claimed in claim 11, wherein a control spring acts between the two sections of the rocker to ensure that the respective sections maintain a contact force on the cam lobe and the valve tip throughout the operating cycle of the rocker system.
13. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is hydraulically operated.
14. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is mechanically operated.
15. An internal combustion engine as claimed in claim 11, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.
16. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.
17. An internal combustion engine as claimed in claim 1, wherein a cam follower is formed in two sections that are slidable relative to one another, one section being cam actuated and the other serving to actuate one of the rockers, sliding of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve.
18. An internal combustion engine as claimed in claim 17, wherein a control spring acts between the two sections of the cam follower to ensure that the respective sections maintain a contact force on the cam lobe and the corresponding rocker throughout the operating cycle of the rocker system.
19. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is hydraulically operated.
20. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is mechanically operated.
21. An internal combustion engine as claimed in claim 17, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.
22. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.
Type: Application
Filed: May 7, 2007
Publication Date: Nov 22, 2007
Inventors: Timothy Mark Lancefield (Shipston-on-Stour), Ian Methley (Witney), Mark Andrew Richard Walton (Westbury)
Application Number: 11/744,964
International Classification: F01L 1/18 (20060101); F01L 1/34 (20060101);